The present invention relates to an AC voltage amplifier, particularly a broadband amplifier for optical communication, comprising a single-gate field-effect transistor to which the input voltage to be amplified is applied at the gate end.
There are prior-art AC voltage amplifiers containing a dual-gate filed-effect transistor which operates in a frequency range of a few hertz to several gigahertz.
A dual-gate field-effect transistor can be thought of as a cascade circuit represented by two single-gate transistors, with the input transistor used in a common-source configuration and the output transistor operating as a gate stage in the turn-on region. Because of its complicated geometrical structure, a dual-gate field-effect transistor has a lower cutoff frequency than a single-gate field-effect transistor used as part of a dual-gate field-effect transistor, and it has a higher input capacitance than such a single-gate field-effect transistor. In a dual-gate field-effect transistor, small currents may occur in the control process which also flow in the gate stage. As a result, the cutoff frequency is reduced.
This AC voltage amplifier does not permit a very large bandwidth and a wide dynamic range.